Composite fiber tape formed of high tensile strength fibers of materials such as boron, graphite, or glass, and impregnated with a matrix of a thermosetting resin, has been employed for a number of years in the manufacture of laminated composite structural shapes for aircraft and aerospace vehicles. Frequently the fibers are all mutually parallel and run longitudinally along the tape. However such composite tape is also available with fibers running transversely or obliquely with respect to the length of the tape. Such oblique fiber tape may be a strip cut on a bias from a wider sheet of composite material. Composite tape structural parts are commonly made by superposing many laminations with different tape or fiber orientations, each lamination made by laying down strips of composite tape, generally in a side-by-side relation upon a pattern or form. Successive and superposed strips and layers will have different fiber orientations. Tape and fiber orientations are chosen to obtain advantage of the high strength characteristics of the fiber. The many laminations are placed in a mold and heated to cure the resin and provide the finished part. Much time, effort, and expense has been devoted to the fabrication of automatic machines for the laying of individual strips of tape. Examples of such tape laying machines are shown in U.S. Pat. Nos. 3,574,040; 3,775,219; 3,810,805; 4,133,711; and 4,292,108.
These machines generally involve an overhead gantry from which is suspended a laterally traveling tape laying head which often carries tape supply and take up reels, guiding mechanisms, cutting mechanisms, a heater, and a tape pressure foot. The tape laying head does all the tape preparation, in addition to pressing the tape upon a work surface. In the head mechanism, tape is withdrawn from a supply reel carried by the mechanism, and cut into predetermined strip lengths as it is applied to a work surface. The composite tape, having an exceedingly high modulus of elasticity, is stiff, inelastic, and difficult to handle. The tape head laying machine is massive, expensive, slow, and complex, and, in some cases, may comprise a structure in the order of one to two feet in diameter and four to six feet in height. All of this structure must be movably mounted on a gantry and controlled for guiding the tapes in precise, aligned side-by-side paths.
An additional problem exists in the laying of tape upon a surface of compound curvature. To properly fit a compound curve, the individual tape fibers, running longitudinally of the tape, must slip longitudinally relative to one another, because those fibers extending over a path of greater curvature must have a greater length than adjoining fibers of the same tape strip that extend over a path of lesser curvature. However, where the tape supply reel is carried by the tape laying machine, and, in particular, where a long strip of tape is not cut until after a portion of the same strip has been laid, no relative slippage of tape fibers is possible.
Imperfections in the manufacture of the tape, or damage to the tape during handling, can be discovered in prior art machines only after the tape has been pulled out of the tape laying machine and at least partly laid upon the work surface. Therefore, a damaged tape strip can be replaced only after it has been laid, a situation that increases cost and time of manufacture, particularly where a damaged strip of tape of many feet or many tens of feet in length must be removed after it has been laid.
Speed of the tape laying operation and application to manufacture of parts of varying configurations are limited by the mounting of tape reels and tape pressure rollers all on the same massive head. The machine gantry must be at least as long as the longest tape path, and thus use for very long parts is not practical.
Accordingly, it is an object of this invention toavoid or minimize above-mentioned problems.